Superconducting materials are characterized by their very desirable ability to conduct electricity without resistance. These superconducting materials can be deposited onto a variety of substrates for use in a variety of applications, including, e.g., conductive wires, tapes, and electronic devices. To be commercially viable, superconducting materials used in these applications must have a high critical current density (Jc) (i.e., the maximum current density a superconductor can carry at a given temperature and magnetic field) because high electrical current is required to power any significant load. It has been shown that superconducting materials formed with biaxially textured crystalline structures have superior critical current densities.
Generally, texturing refers to a cluster structure comprising a number of crystal particles that have the same crystal orientation (e.g., longitudinal axial direction) in a polycrystalline or other material. Biaxial texturing describes material in which a significant number of the crystal particles in the cluster structures are oriented generally uniformly in all of the three axes. When viewed under a microscope, biaxially textured superconductor materials appear to have numerous, elongated, crystalline structures oriented in a common longitudinal direction.
It is now well established that biaxially textured crystalline substrates are critical to obtaining superior critical current densities (Jc) for YBa2Cu3O7-δ (YBCO) superconductors. One way to accomplish biaxial texturing in a superconducting material is to grow epitaxial YBCO onto biaxially textured substrates. Rolling-assisted biaxially textured substrate technology has also proven to be very promising for fabricating YBCO-coated conductors that can support large currents in high magnetic fields at 77 K.
In any case, buffer layers are the key component in YBCO superconductors based on rolling-assisted biaxially textured substrates, such as, Ni and nickel alloys. These buffer layers provide a chemically inert, continuous and smooth base for the growth of the YBCO layer, while transferring the biaxial texture from the substrate to the high-temperature superconductor (HTS) layer. Buffer layers also act as barriers to prevent the diffusion of metal to the HTS layer and oxidation of the metal substrate, because YBCO is processed at about 800° C. in an oxygen atmosphere of 100 ppm or more.
Recently, more attention has been given to paramagnetic Ni—W substrates to improve mechanical properties and reduce magnetism. Growth of oxide buffer layers directly on textured paramagnetic Ni—W substrates under typical conditions is challenging because the localized formation of tungsten oxide can deteriorate the properties of oxide buffer layers and YBCO layers. Currently, Ni—W substrates are sulfurized to form a protective sulfide surface layer. Commercial-quality buffer-layer architectures deposited on sulfurized Ni—W are typically CeO2/YSZ/Y2O3/Ni—W and CeO2/YSZ/CeO2/Ni—W. At present, the buffer layers are typically deposited by direct current (DC) magnetron sputtering and pulsed-laser deposition (PLD), which operate at relatively slow deposition rates.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those of skill in the art upon a reading of the specification and a study of the drawings.